plane-strain work hardening and transient behavior of interstitial-free steel

Abstract

Stress transients resulting from abrupt changes in strain path have been shown to be important to subsequent formability. In order to investigate whether these transients result from strain aging or related interstitial effects, two-stage experiments were performed on Armco interstitial-free steel After a prestrain in plane-strain tension, the material was strained in uniaxial tension in the direction of zero initial extension. The stress-strain curve in plane strain was found to deviate markedly from that predicted by usual plasticity theory (Hill’s theory withM = 2.0). Comparison of monotonie curves from uniaxial and plane-strain tension using a newly-developed, self-consistent calculation suggested that IF steel follows Hill’s new theory with constantM ≈ 2.9. After the change from plane strain to uniaxial tension, positive stress transients (flow stress exceeds the monotonie flow stress) were measured. This form of transient agrees with ones measured for other steels. It therefore appears that the origin of the transient phenomenon is independent of interstitial content, and that static strain aging is not the mechanism by which these stress transients occur.